In general, interior materials of a vehicle may be required to have reduced weight properties and high rigidity, dimensional stability, moldability, low manufacturing cost, and the like. Further, reduced weight and recyclability of vehicle parts may have greater significance due to recent enforcement of environmental regulations on vehicles, the depletion of petroleum resources, and the like.
The interior materials of a vehicle may be used for a door trim, a filler, a door scope, a package tray, and the like, and these interior materials may vary in the material and constitution thereof depending on types of vehicle. Meanwhile, a rigid substrate in the constitution has been typically manufactured by an injection molding process using a polypropylene composite resin. The rigid substrate for the vehicle interior materials manufactured by injection molding may have improved rigidity and recyclability, but may have a limitation on weight reduction, and sink marks and the like may be generated on the surface of the molded product, thereby deteriorating marketability thereof.
Polypropylene resins are a typically used plastic having a substantially greater strength than those of other resins, and improved mechanical properties and recyclability, and these characteristics may be due to crystallinity of the polypropylene molecules and the molecular structure of the polymer chains. Furthermore, the polypropylene resins may have substantial resistance to deformation at elevated temperatures and have substantial tensile strength and surface rigidity, and further a polypropylene composite resin may be manufactured with further improved physical properties by using an impact modifier or an inorganic filler for reinforcement according to the use thereof.
While having these excellent physical properties, the polypropylene resins may have less foamability than other resins due to weak melt tension due to linear chain structure thereof, and thus production of a foam body may be limited. In general, when the melt tension is low, cell walls which separate gas may not be strong enough to overcome the tension such that cell walls may be easily collapsed and ruptured. Therefore, the foamed product may have a high ratio of collapsed cells and the cell structure may not be controlled, thereby deteriorating moldability thereof.
In the related arts, a material for foam injection has been developed and the material may be manufactured by using a high-impact propylene resin, rubber, and an inorganic filler. However, expansion ratios of the material may not be sufficient and the process costs may increase because an expensive chemical foaming agent is used for foaming, or conditions for physical foaming process may not be controlled easily.
In other related arts, a modified polypropylene resin composition with improved bubbling property and a foam body prepared by using the modified polypropylene resin composition have been introduce. The polypropylene composite resins, however, fail to have a sufficient degree of crosslinking, and thus, industrialization of the resins has not been achieved. Moreover, industrial advantages have not been provided because the produced foam body may need to be compressed repeatedly and formed to make an interior material of a vehicle.
As such, there is an unmet need for developing a rigid substrate for interior and exterior materials of a vehicle, which may improve physical properties such as high rigidity and a light weight.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.